The invention relates generally to neutron tubes, and more specifically to neutron tubes based on plasma ion sources.
Conventional neutron tubes employ a Penning ion source and a single gap extractor. The target is a deuterium or tritium chemical embedded in a molybdenum or tungsten substrate. Neutron yield is limited by the ion source performance and beam size. The production of neutrons is limited by the beam current and power deposition on the target. In the conventional neutron tube, the extraction aperture and the target are limited to small areas, and so is the neutron output flux.
Commercial neutron tubes have used the impact of deuterium on tritium (D-T) for neutron production. The deuterium-on-deuterium (D-D) reaction, with a cross section for production a hundred times lower, has not been able to provide the necessary neutron flux. It would be highly desirable and advantageous to make D-D neutron sources. This will greatly increase the lifetime of the neutron generator, and it would greatly reduce transport and operational safety concerns.
Brachytherapy is a type of radiation therapy in which radioactive materials are placed in direct contact with the tissue being treated. The currently available fast neutron source for brachytherapy treatment of tumors is a spontaneous fission source such as the radioactive isotope Cf-252 which is implanted into a patient. All present U.S. Cf-252 neutron source designs require manually afterloaded systems. Because Cf-252 is a radioactive source, it cannot be turned off to prevent excessive exposure of clinical personnel. The average energy of the spontaneous neutrons emitted from a Cf-252 source is 2.3 MeV which is very close to the energy of a D-D neutron source, 2.45 MeV. By utilizing a D-D neutron tube which can be turned on and off, the patient can be subjected to radiation treatment at desired times, and clinical personnel will receive no occupational dose from the source while it is turned off during patient preparation.
The utilization of in-situ fast neutrons in treating radioresistant tumors has been demonstrated to be more effective than external neutron sources where the neutrons have been slowed down while penetrating the body. Since the dose is delivered to the tumor by fast neutrons, it is not necessary to inject any drug for the delivery of neutron absorbing boron into the tumor, as is often done to increase the capture of slow neutrons. However, boron can be used to enhance the dose delivery to neighboring metastases. Therefore, another advantage of a fast neutron brachytherapy source over an external source is its capability of tailoring the dose distribution around the region of the tumor.
Therefore, a miniaturized implantable neutron generator design adapted for brachytherapy would be highly advantageous.
It would also be desirable, in many other applications such as cargo screening, airport luggage screening, and explosives detection, to have a sealed tube neutron generator which provides a high neutron flux with long life operation and with variable source size. The neutron generator would overcome many of the shortcomings of the presently available neutron tubes.